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G Asch

Publications and source records attributed to G Asch.

31 records · Page 2Linked to original sources
PubMedDate not supplied

Subduction and collision processes in the Central Andes constrained by converted seismic phases.

The Central Andes are the Earth's highest mountain belt formed by ocean-continent collision. Most of this uplift is thought to have occurred in the past 20 Myr, owing mainly to thickening of the continental crust, dominated by tectonic shortening. Here we use P-to-S (compressional-to-shear) converted teleseismic waves observed on several temporary networks in the Central Andes to image the deep structure associated with these tectonic processes. We find that the Moho (the Mohorovicić discontinuity--generally thought to separate crust from mantle) ranges from a depth of 75 km under the Altiplano plateau to 50 km beneath the 4-km-high Puna plateau. This relatively thin crust below such a high-elevation region indicates that thinning of the lithospheric mantle may have contributed to the uplift of the Puna plateau. We have also imaged the subducted crust of the Nazca oceanic plate down to 120 km depth, where it becomes invisible to converted teleseismic waves, probably owing to completion of the gabbro-eclogite transformation; this is direct evidence for the presence of kinetically delayed metamorphic reactions in subducting plates. Most of the intermediate-depth seismicity in the subducting plate stops at 120 km depth as well, suggesting a relation with this transformation. We see an intracrustal low-velocity zone, 10-20 km thick, below the entire Altiplano and Puna plateaux, which we interpret as a zone of continuing metamorphism and partial melting that decouples upper-crustal imbrication from lower-crustal thickening.

Journal Article↗
PubMedDate not supplied

Performance and sensitivity of modern home pregnancy tests.

We have studied the performance of three currently available home pregnancy tests. The Advance is a test based on monoclonal antibodies in an enzyme immunoassay format that specifically detects hCG in urine. The positive results are determined by the presence of a blue color in a color stick (30 minutes). The Daisy 2 and FACT are tests based on monoclonal antibodies that specifically detect hCG in urine in a hemagglutination inhibition assay; positive results are demonstrated by the deposition of a dot ring at the bottom of the test tube (45 minutes). Thirty-five patients who eventually became pregnant in that cycle collected the first morning urine specimens from day of ovulation (determined by ultrasound) in artificial insemination donor (AID) cycles, or from the date of gamete intrafallopian transfer (GIFT) for 16 consecutive days. In each specimen, the Advance, Daisy 2, and FACT tests were performed; in addition, beta-hCG levels were determined by radioimmunoassay. All the home pregnancy tests studied can detect pregnancy as early as 9 or 10 days post-conception, and they give positive results at the time of the expected onset of menses in 70%, 95%, and 88% of cases for Daisy 2, Advance, and FACT, respectively. The sensitivity of the these home pregnancy tests was determined to be about 200 mIU/mL of urine after correlating their positive or negative results with the concentrations of urinary beta-hCG determined by radioimmunoassay.

Antibodies, Monoclonal↗